The world “control” is used for a lot of different things and sometimes we even think negatively about it. But, control can be very useful, in some cases even essential and it is all around is. Here are some examples:
Your blood sugar level describes how much blood is currently in your blood. Through the blood the sugar is transported to the cells all around your body and allows them to work properly. If that works, great! But if the blood sugar is too low or too high, your body will not work properly, you might feel dizzy or worse. Fortunately, in most people, the body “controls” the blood sugar level by constantly sensing it and adjusting it in case it is too low or too high to always bring it back into a healthy range.
In another example let’s consider that you want to balance a pen or stick on your hand. Place the stick or pen upright on the flat palm of your hand. If you don’t do anything, it will simply fall down of course. But through moving your hand fast enough in the correct direction, one can prevent the stick/pen from falling and hence balance it on the hand. This is also control!
The principle of control is a feedback loop that combines sensing, comparing, control and actuation:
Sensing: one measures or senses what is to be controlled, in the examples above the blood sugar is sensed through appropriate parts of the human body and when trying to balance a stick or pen, we sense its position by looking at it
Comparing: the actual value or state is then compared to the desired level to compute the difference between the two, in the first example above, the body has a healthy (range of) blood sugar and checks whether your blood pressure is currently too low or too high, in the second example you see if and how much the stick/pen is tilted and in which direction and you directly see the difference to the desired value, which would be standing perfectly upright on the palm of your hand
Control: the “controller” then takes the result form the previous comparison and decides what to do about it, for instance the body has to decide how much insulin to release in order to bring the blood sugar to the desired range or value; and the for balancing a stick or a pen, one has to quickly decide how exactly to move the hand based on the current position of it
Actuation: an “actuator” is something that produces the actual change in the system, for example the actuator for controlling your blood sugar are the cells in your body producing and releasing the right amount of insulin; when balancing the stick or pen, the actuator is your hand that you move to balance
Feedback: all these steps and parts above work simultaneously and constantly sense, compare, control and actuate. Because the action of the actuator changes the state of the system, e.g. your blood sugar or the position of the pen, the feedback loop is constantly active by sensing the change in the state, comparing it to the desired value, controlling it and acting again accordingly. All this happens in a feedback-loop.
Automatic control is the science to understand how such loops work, where we find them around us and what we can do to use this idea to make the world a better place. For example automatic control is used to
- control the blood sugar of people with diabetes, where the natural control in the body does not work anymore
- control a segway so that one go on a ride through town – this is actually very similar to balancing the pen or stick on your hand!
- control the temperature in your oven when baking cookies
- control the position of an (self-driving car) car on the road to make sure it drives at the correct velocity and stays on the lane
- control the movement of a plane to ensure you have a safe and smooth flight
- control the temperature of a reactor to ensure it runs as expected
And control can also be found in many more cases all around you. Do you want to learn more? Join us at one of our workshops!